historical stuff in math(3)
Thomas David Rivers
rivers at dignus.com
Thu Jan 22 03:57:40 PST 2004
> On Wed, Jan 21, 2004 at 06:41:49AM -0500, Thomas David Rivers wrote:
> >> Isn't all the vax-D format related stuff math(3) getting pretty old ?
> > It's very similar to the IBM mainframe format. So, a port
> > of FreeBSD to the IBM mainframe could still use it. (The VAX
> > format was just a copy of the IBM one with an extra precision bit
> > thrown in every now-and-then.)
> Not really. The IBM S/360 uses base-16 whereas virtually everyone
> else (including VAX) uses binary. The S/360 double precision format
> has a 14-digit (56-bit) fraction (no implicit digit), a fraction sign
> and a 7-bit signed exponent. The VAX-D documentation in math(3) is
> totally irrelevant to the S/360. Any serious math library would need
> significant re-work to handle the increased range and reduced/variable
My bad... I thought the VAX code was base-16 as well. I could
be confusing it with the Data General MV series...
> Someone else mentioned the Alpha - VAX-format FP is specified in
> the architecture to simplify migration from the VAX. The early chips
> included it in hardware - do the recent chips still include it?
> > But - even the mainframe has an available/alternate IEEE format now,
> > and the mainframe version of gcc uses that...
> I think this must be new in the S/390. It's definitely not part of
> the S/360 or S/370 families and I don't believe it existed on the 30xx
> or 43xx families.
Yes - new will ALS 1 (Architectural Level Set #1). If your
OS/390 operating system is new enough (past 1992 I think?), it will
emulate the new IEEE instructions if your hardware doesn't have
them. Linux will do the same thing.
The mainframe has evolved quite a lot since the 360. The new
z/Series machines are serious 64-bit Linux contenders.
But - I'm getting off-topic...
- Dave R. -
rivers at dignus.com Work: (919) 676-0847
Get your mainframe programming tools at http://www.dignus.com
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